1. Field of the Invention
This invention relates to a process for the preparation of lithium diphenylphosphinobenzene-m-monosulfonate.
2. Description of Prior Art
Japanese Patent Application Laid-open KOKAI No. 58-131994 discloses a process for the preparation of lithium diphenylphosphinobenzene-m-monosulfonate which comprises sulfonating triphenylphosphine, extracting the products with 4-methyl-2-pentanone, neutralizing and extracting the same products with an aqueous solution of lithium hydroxide, and evaporating the resulting aqueous layer to recover lithium diphenylphosphinobenzene-m-monosulfonate.
U.S. Pat. No. 4,483,802 discloses a process for the preparation of diphenylphosphinobenzene-m-monosulfonate which comprises sulfonating triphenylphosphine to form a sulfonation mixture, diluting said mixture with water to form an aqueous solution, extracting said aqueous solution with an organic solution of a water-insoluble amine in a water-insoluble organic solvent, separating the resulting organic solution, mixing said organic solution with an aqueous solution of a base to form a basic aqueous layer, separating said basic aqueous layer and recovering diphenylphosphinobenzene-m-monosulfonate.
U.S. Pat. No. 4,142,060 describes a process for the preparation of a salt of tri(m-sulfophenyl) phosphine which comprises treating an aqueous solution of sodium tri(m-sulfophenyl) phosphine with a strongly acidic cation exchange resin, eluting the products with water, reacting the formed acidic aqueous solution with a base to form the other salt of tri(m-sulfophenyl)phosphine.
The problem which arises during carrying out the process for isolating the product from the sulfonation mixture by extraction is the contamination with lithium sulfate in the neutralized aqueous solution because sulfuric acid is simultaneously extracted in the aqueous solution. According to the process using ion exchange resin, the obtained product is colored in the ion exchange reaction. And this process is uneconomic due to tedious procedures such as conversion procedure of the product to its free acid. Lithium diphenylphosphinobenzene-m-monosulfonate cannot be recrystallized from an aqueous solution because of its high solubility in water, the solubility being quite different from that of sodium diphenylphosphinobenzene-m-monosulfonate.
In a catalytic reaction using a noble metal complex, lithium diphenylphosphinobenzene-m-monosulfonate used as a ligand is required to be in high purity.
Consequently, an industrial process for advantageously producing lithium diphenylphosphinobenzene-m-monosulfonate is required.